This project has three aims. The first is development, refinement, and testing of an explicit theory of language acquisition in children. The theory, building on earlier work, will if successful account for the development of language from the start of syntax learning through the acquisition of complex grammatical structures; it will be consistent with linguistic theory and the important facts of language development in children; it will deal with exotic languages as well as English; and it will learn despite noisy, complex, misinterpreted, or nonstandard inputs. A computer simulation of the theory, using "constraint satisfaction" algorithms from artificial intelligence research, will test its adequacy and claims about the kinds of information necessary and sufficient for language acquisition to work. The second aim is to search computerized databases of children's speech for "possible but nonoccurring errors", such as violations of subjacency or dative movement. These searchers will be used to test claims about what sorts of linguistic constraints children are born with. The third part of the project is an experimental investigation of certain of children's rule-learning mechanisms and their cognitive correlates. Children will be taught novel words in isolation to see if they use the semantics of a word to guess its syntactic privileges (e.g. action word = verb; agent = subject). Interactions between conceptual structure and language development will be examined by studies examining the acquisition of constraints on the causative construction, children's use of a "thematic" or spatial schema to conceptualize nonspatial events such as changes of state, and their acquisition of spatial and nonspatial prepositions. Results of the project could yield new methods of assessing children's ability to produce specific grammatical constructions, insight into the language learning mechanisms that can be used in remediation programs for language-disabled individuals, specific techniques to teach new words and constructions to children, and quantitative measures of language development.